In current disk drive systems that employ flying heads, there is a protective film of air between the head and the disk, where no contact is intended to occur during head read/write operations. The read/write head is typically a part of or affixed to a larger body that flies over the disk and is typically referred to as a “slider.” The slider also includes a surface referred to as an air bearing surfaces (ABS). The ABS has aerodynamic effects such as compression or expansion of air to generate positive or sub-ambient pressure. The ABS may include a flat surface, step, cavity, and/or taper. The ABS may also be referred to as a rail in the industry. The slider's body is attached to a suspension arm via a head gimbal assembly that biases the slider body towards the disk. The net effect of the ABS and the suspension arm is to cause the slider to fly at the desired height when the disk is at full speed. During normal flying conditions, the slider maintains a positive pitch attitude as illustrated in FIG. 1A.
Continuous improvements have been made in increasing the areal density (i.e., the number of stored bits per unit of surface area) of the magnetic recording disks. As is well known, decreasing the fly height of the read/write element (head), for example, results in reduced PW50 (the pulse width where the read head output amplitude, in response to an isolated transition, is 50% of the peak value) that allows for greater recording density. Bringing the head closer to the media has been a key area of effort in increasing recording densities.
As the fly height of a head in disk drive systems decreases, the probability of intermittent contacts between the slider and the disk surface increases. The friction generated between the disk and the trailing edge of the slider may cause a pitch low attitude that can lead to “choking” of the ABS. Once the air supply to the ABS becomes insufficient, the slider stalls resulting in head contact with the disk surface that may be exacerbated by slider vibrations. This is particularly problematic when the disk surface is very smooth and the friction force becomes sufficient to give enough force to the slider to pitch down resulting in a negative pitch attitude as illustrated in FIG. 1B.
One solution to reduce head contacts is to add stability to the slider by designing an air bearing with low pitch attitude. One problem with such a solution is that even if the slider has good stability, it may not be sufficient to prevent the contact especially during extreme conditions such as low RPM servo-writing or high altitude operation. Because the slider is supported by the air bearing and the trailing edge that contacts the disk is pulled by the frictional contact force, the slider tips over such that the pitch angle of the slider can be made negative. Once this condition occurs, the slider may not be easily recovered. The slider oscillations from tip over and attempted recovery may produce slider collisions with the disk surface potentially resulting in damage to the read/write head element and/or data surface of the disk. Further, the slider oscillations cause servo writing failures due to the production of an unstable signal.
Other solutions intended to reduce friction when slider contacts occur in contact-start-stop (CSS) drives include texturing the slider, design a slider having a positive crown (longitudinal curvature to the air bearing surface contour), or using multiple pads on the ABS of the slider. CSS drive systems dedicate a portion of the disk's surface, referred to as the CSS zone, for the slider to reside when the drive is not in operation. With this type of system, the slider directly contacts the disk's surface in the CSS zone.
Although such solutions may reduce the friction between the slider and disk surface in CSS drives, they may not be able to prevent negative pitch conditions from occurring. In particular, some prior solutions in CSS drives utilizing multiple pads may not prevent a negative pitch attitude of the slider because the height of the pads with respect to the disk surface is equal, thereby resulting in zero pitch angle that positions the slider in an unstable attitude, as illustrated in FIG. 1C. Other prior solutions in CSS drives utilize a protrusion located centrally off the forward portion of a slider that projects below the air bearing surface, as illustrated in FIG. 1D. The protrusions have been disposed either on a frontal ramp (tapered) section of a slider or aft of such a ramp section. The protrusion provides a positive pitch when the slider is at rest on a stationary disk. The intent of the protrusion is to reduce the stiction force between the slider and the disk surface when the slider is lifted off of the disk's surface. Therefore, such a protrusion may not be sufficient in preventing negative pitch attitude of the head in operation and may not be optimum for use in a load/unload disk drive system that requires no contact between a slider and disk.